Conventionally, polymerized products of an aromatic diisocyanate such as diphenylmethane diisocyanate (MDI), tolylene diisocyanate (TDI), etc., have been known as an aromatic polycarbodiimide. Such an aromatic polycarbodiimide has been used as flame and fire resistant films and heat resistant adhesives due to its excellent heat resistance.
A film of a conventionally known aromatic polycarbodiimide has a heat resistance in the point that even when the film is exposed to high temperature of higher than 400.degree. C., the film does not form a volatile gas and decomposed monomers. However, when the film is subjected to a heat treatment at a temperature of higher than 200.degree. C., the film loses the self-retention property and becomes brittle, thereby the film cannot endure the practical use. Further, the film has a low moisture resistance at high temperature and high pressure.
A conventional polymer induced from a known aromatic diisocyanate has the disadvantages that since the polymer has a high melting point, a melt-molding thereof is difficult, and film forming from the polymer solution is difficult because they have low solubility to organic solvents. Further, it may be difficult to generally produce a polymer having a high degree of polymerization for the conventional aromatic diisocyanate. Also, to obtain the mechanical characteristics of the polymer suitable for films and moldings, a divalent aromatic residue in the polymer skeleton must be a p-substituted bond, but such a polymer skeleton has a rigidity and is poor in flexibility.